The reducing of the operating power in a puffer type circuit breaker, which is at present the most widely used gas circuit breaker, has generally been done by employing a structure consisting of a combination of a puffer system and a self-actuated arc-extinguishing system in which the arc heat is positively utilized to increase the gas pressure and reduce the gas-compressing external force. In the puffer type circuit breaker, a double flow system in which a high pressure gas is blown against both the stationary portion and the movable portion is an essential technique for a large current circuit breaking operation. This kind of puffer type gas circuit breaker is disclosed, for instance, example, U.S. Pat. No. 3,839,613.
In accordance with these facts, a puffer type gas circuit breaking structure shown in FIGS. 1 to 3 in which a gas pressurized by arc heat is blown effectively against the arc by utilizing a double flow system has been proposed by the inventors of the present patent application.
Referring to FIGS. 1 to 3, an insulated or grounded closed metal container 1 has an interior 2 filled with an arc-extinguishing gas such as SF.sub.6 gas. A shaft portion 5 of a fixed element body 4, of an electrically conductive material, is fixed at one end 6 thereof to an end wall 3 of the closed container 1. The fixed element body 4 includes a central fixed element portion or fixed arc contactor portion 9 extending in an axial direction A from the center of a flange portion 8 formed at the other end 7 of the shaft portion 5, and a hollow cylindrical main fixed element portion 10 extending from the circumferential edge of the flange portion 8 in the axial direction A.
A frame body 11 is stationarily fixed to the closed container 1 like the fixed element body 4. The frame body 11 has a cylindrical base portion 13 of large thickness having a central hole 12. A hollow cylindrical puffer piston portion 15 is formed so as to extend from a radially inner edge portion of an end portion 14 of the base portion 13 in an axial direction B. The cylindrical piston portion 15 has a hole 16 coaxial with and of the same diameter as that of the central hole 12. A cylindrical portion 17 of medium diameter is formed to extend from a radially outer edge portion of the end portion 14 of the base portion 13 in the axial, direction B, with a flange portion 18 extending radially outwardly from the end of the medium-diameter cylindrical portion 17, and an exhaust gas guide 19 of large diameter extending from the outer edge of the flange portion 18 in the axial direction B. circumferentially equidistantly, in the large-diameter exhaust gas guide 19 serving as block means, at the auxiliary predetermined position C thereof.
A movable part 21 of an electrically conductive material, is movable in the axial directions A and B with respect to the fixed element body 4. The movable part 21 has an operating shaft 24 fixed at one end 23 thereof to an operating device or actuator 22 and extends from the end 23 in the axial direction B while slidably passing through the holes 12, 16 of the frame body 11. The shaft portion 24 is formed at the other end 25 thereof with a hollow conical portion 26 extending radially outwardly from the end 25 in the direction B. The conical portion 26 is curved smoothly at a tip end 27 thereof for permitting gas to flow smoothly in a manner described more fully hereinbelow. An outer edge portion 28 of the conical portion 26 is bent radially outwardly and brought into gastight contact with an inner peripheral surface 29 of the large-diameter exhaust gas guide 19 of the frame body 11 in the closed state of FIG. 1. A cylindrical portion 31, serving as a puffer cylinder, extends from an intermediate portion of the inside surface of the conical portion 26 in the axial direction A and is fitted around the cylindrical piston portion 15 of the frame body 11 so as to define a cylindrical puffer chamber 30 in cooperation with the outer peripheral surface of the shaft portion 24. The conical portion 26 is formed with a hole 32 which opens into the chamber 30 so that, when the movable part 21 is moved in the direction A with respect to the frame body 11, the compressed gas flows out of the chamber 30 with the insertion of the piston portion 15 into the chamber 30 in the direction B.
Further, a hollow cylindrical movable contactor portion or movable arc contactor portion 33 is extends from the end of the shaft portion 24 in the axial direction B. The cylindrical movable contactor portion 33 is fitted around the central fixed element portion 9 in the inoperative state, that is, in the closed state (FIG. 1), and, when the movable part 21 is moved in the direction A with respect to the fixed element body 4, electric contact is released. The movable contactor portion 33 is formed in the outer peripheral surface thereof with concave portions 34 at a position close to the tip end, and ring springs 35 are provided in the concave portions 34. A space 36, defined inside the movable contactor portion 33 conically diverges at a part 37 thereof close to the curved end 27 of the shaft portion 24.
A cylinder 38 of large diameter, the tip end of which serves as a main movable element, extends in the axial direction B from the outer edge portion 28 of the conical portion 26. The large-diameter cylinder 38 of the movable part 21 is fitted in a gas-tight manner in the large-diameter exhaust gas guide 19 of the frame body 11. The large-diameter cylinder 38 is formed with a plurality of openings 39 circumferentially equidistantly at the position thereof in the vicinity of the outer edge portion 28. A passage 40, extending radially outwardly from the conical chamber 37 in the movable contactor portion 33, is formed between each of the openings 39 and the conical chamber 37. These passages 40 are defined by the conical portion 26 and a plurality of internal wall portions 41 each extending obliquely, so that each passage 40 is inclined with respect to the radial direction so as to smooth the flow of gas from the chamber 36. The passages 40 serve as exhaust passages, and the openings 39 serve as exhaust ports.
A nozzle 42, consisting of an electrically insulating material, comprises a hollow cylindrical large-diameter portion 43, a nozzle main body portion 45 of small diameter having a nozzle hole 44, and an intermediate portion 46 for connecting the large-diameter portion 43 with the main body portion 45. The nozzle hole 44 includes a cylindrical hole portion 47 as a throat portion into which the central fixed element portion 9 is fitted in a gas-tight manner, and a conical hole portion 48 extending outwardly therefrom. One end 49 of the large-diameter portion 43 of the nozzle 42 is brought into a gastight engagement with the inside groove formed in an expanded end portion 50 of the large-diameter cylindrical portion 38 of the movable part 21, so that the nozzle 42 cooperates with the large-diameter cylindrical portion 38, the internal wall portions 41, the conical portion 26 and the movable contactor portion 33 of the movable part 21 to define an expansion chamber 51 in which the gas heated and compressed by the arc is stored or accumulated.
In addition, the fixed element body 4 and the movable part 21 are arranged in series in an AC line of 50 to 60 Hz, for example, through terminals 52 and 53. In the inoperative (closed) state of a circuit breaker 60 of the above construction, an electric current flows between the terminals 52 and 53 through electrical connections between the central fixed element portion 9 and the movable contactor portion 33 which are in contact with each other and between the main fixed element portion 10 and the large-diameter cylindrical portion 38 of the movable part 21 which are in contact with each other as shown in FIG. 1.
In breaking the electrical connection between the terminals 52 and 53, the circuit breaker 60 is operated in the following manner.
First, upon receipt of an instruction (signal) to interrupt the current, the operating device 22 is actuated to cause the shaft portion 24 of the movable part 21 to move in the direction A with respect to the fixed element body 4 and the frame body 11. This movement first breaks the electrical connection between the main fixed element portion 10 and the large-diameter cylindrical portion 38 of the movable part 21, but the central fixed element portion 9 and the movable contactor portion 33 are kept in contact with each other. The movement of the movable part 21 in the direction A causes the cylindrical piston portion 15 of the frame body 11 to be moved relatively into the puffer chamber 30 in the direction B, so that the pressure of gas in the puffer chamber 30 and the expansion chamber 51 communicated therewith is increased.
Further movement of the shaft portion 24 in the direction A causes the central fixed arc contactor portion 9 to slip out of the movable contactor portion 33, thus starting parting of the movable contactor portion 33 from the central fixed arc contactor portion 9. As a result, the arc discharge 61 starts to take place between the central fixed arc contactor portion 9 and the movable contactor portion 33. During an initial stage of such breaking operation, the central fixed arc contactor portion 9 still closes the hole 47 of the nozzle 42 so that relative insertion of the cylindrical piston portion 15 of the frame body 11 into the puffer chamber 30 in the direction B causes the increase of the pressure of the gas not only in the puffer chamber 30 and the expansion chamber 52 but also in the chamber 36 defined inside the movable contactor portion 33 in communication with the expansion chamber 51 and the exhaust passages 40 the openings 39 of which are closed by the cylindrical portion 38 serving as the block means. In addition, the arc 61 produced between the central fixed arc contactor portion 9 and the movable contactor portion 33 causes the gas in the expansion chamber 51 and the chamber 36 inside the movable contactor portion 33 to be heated, resulting in the increase of the pressure of the gas in the expansion chamber 51.
In case that the electric current to be interrupted is relatively small, since the arc 61 heats the gas to a relatively low degree, the gas is not so much heated nor compressed by the arc 61 but the gas in the chambers 30, 51, 36 and 40 has been compressed to reach a certain level of pressure due to insertion of the piston 15 into the puffer chamber 30. Consequently, as shown in FIG. 2, when a further movement of the movable part 21 in the direction A causes the central fixed arc contactor portion 9 to slip out of the throat-like cylindrical hole 47 of the nozzle 42, the gaseous plasma of the arc discharge 61 is cooled by the gas flow 62 flowing out of the expansion chamber 51 through the throat-like hole portion 47, that is, by means of pufferring of the gas flow 62, resulting in that the electric resistance in this gaseous region is increased to extinguish the arc discharge 61 at a timing close to the zero-cross point of an instantaneous magnitude of AC electric current where the arc 61 is thin, thereby breaking the electrical connection between the central fixed arc contactor portion 9 and the movable contactor portion 33.
In the circuit breaker 60, since no exhaust passage is formed in the shaft 24, unlike the conventional circuit breakers, the shaft 24 can be formed relatively small in diameter. In addition, only a small amount of gas is required for pufferring in regard to a small current, so that the diameter of the puffer chamber 30 formed around the shaft 24 of relatively small diameter can be made relatively small as well, resulting in that the cross-sectional area of the puffer chamber 30 is reduced and, therefore, the operating force exerted by the operating device 22 can be reduced.
On the other hand, in case that the electric current to be interrupted is large, the gas continues to be heated and compressed by the arc 61 until the central fixed arc contactor portion 9 slips out of the throat hole portion 47 of the nozzle 42 as shown in FIG. 2, and however, it is impossible to extinguish the arc 61 by cooling it using only pufferring of the gas flow 62 passing through the throat hole portion 47 of the nozzle 42. However, when the movable part 21 is further moved in the direction A to bring the breaking operation in its intermediate stage as shown in FIG. 3, the central fixed arc contactor portion 9 comes out of the conical hole 48 of the nozzle 42 and the exhaust ports 39 of the exhaust passages 40 are moved to the position C so as to be perfectly communicated with the openings 20 of the large-diameter cylindrical portion 19 as the block means. Consequently, the gaseous plasma of the arc discharge 61 is cooled by two gas flows, that is, double flows including the gas flow 62 flowing through the throat-like hole portion 47 from the puffer chamber 30 and the expansion chamber 51 the pressure in which has been increased and the gas flow 63 flowing from the expansion chamber 51 through the chamber 36, the exhaust passages 40 and the openings 39, resulting in that the electric resistance in this arc region is increased to extinguish the arc 61 at a timing close to the zero-cross point of the instantaneous magnitude of AC electric current, thus breaking the electrical connection between the central fixed element portion 9 and the movable contactor portion 33. The time from receipt of breaking instruction to extinguishment of the arc 61 is substantially equal to the time during which the instantaneous AC current value becomes zero twice (about 1/50 to 1/60 sec., for example).
In the circuit breaker 60, since the exhaust passages 40 are arranged to extend radially outwardly between the movable contactor portion 33 and the puffer chamber 30, unlike the conventional circuit breakers, the length of the exhaust passage 40 can be reduced independently of the length of the puffer chamber 30. Consequently, the flow resistance of the exhaust passage 40 to the gas flow 63 discharged through the exhaust passages 40 and the openings 39 can be reduced so that the gas flow 63 can be made sufficiently large at the timing shown in FIG. 3, thereby assuring more reliably the extinguishment of the arc 61 using the gas flow 63 in cooperation with the gas flow 62.
In the circuit breaking operation in the early stage shown in FIG. 2, an arc 61 occurs between the fixed are contactor portion 9 and the movable contactor 33, and an arc-extinguishing gas in the cylinder, 38 and the puffer chamber 30 is thereby heated. Since the opening 39 on the side of the movable contactor 33 is closed by the exhaust gas guide 19, a wasteful gas flow does not occur at this time.
In the circuit breaking operation in the intermediate stage shown in FIG. 3, when the fixed arc contactor portion 9 out of the insulating nozzle 42, the opening 39 on the side of the movable portion also comes out of the exhaust gas guide 19, and gas flows in the both directions occur simultaneously to extinguish the arc 61.
According to the gas circuit breaker shown in FIGS. 1 to 3, the double flow system capable of carrying out an effective gas blowing operation can be obtained by virtue of the decrease in the flow passage resistance and the increase in the degree of freedom of setting the surface areas of the flow passage and opening 39, which are attributed to the success in reducing the length of the gas flow passage 40 on the side of the movable section.
However, the gas circuit breaker shown in FIGS. 1 to 3 has the following drawback encountered when the voltage in the circuit breaking section needs to increased and the size needs to be reduced.
In order to increase the voltage in the circuit breaking section, it is necessary that the distance L between the main stationary member 10 and the exhaust gas guide 19 in a circuit breaking state must be large as shown in FIG. 3. However, in order to increase the distance L, the positions of the front end of the exhaust gas guide 19 and the opening 39 have to be shifted to the side of the movable section. This causes the longitudinal length of the circuit breaking structure to increase. This contradicts the requirement the circuit breaking section must be reduced. Furthermore, the length of the gas flow passage 40 also increases, so that the flow passage resistance increases and the circuit breaking performance lowered.
Additionally, the fixed arc contactor portion 9, the movable contactor 33 and the insulating nozzle 42 can not easily be replaced because the distance L is too short, and the opening 39 cannot easily be inspected.